Nasal Cavity & Paranasal Sinuses Review

Anatomy Overview

• Pair of nasal cavities serve dual purposes:

  • Inspiration & conditioning of air (respiratory function).

  • Olfaction (special sense of smell).

• Cavities divided functionally into two vertical zones on each side:

  • Lower \frac{2}{3} = Respiratory region.

  • Upper \frac{1}{3} = Olfactory region (olfactory mucosa with olfactory bulb projections).

• Deeper inspiration drives more air toward the olfactory mucosa, enhancing smell detection.

Functional Zones & Mucosae

• Respiratory Region (inferior \frac{2}{3}):

  • Air contacts highly vascular mucosa → warming & humidification.

  • Protective preparation before air reaches lungs.

• Olfactory Region (superior \frac{1}{3}):

  • Contains olfactory epithelium.

  • House olfactory nerve endings projecting through cribriform plate to olfactory bulbs.

Bony & Cartilaginous Framework

• Nasal Septum (medial wall)

  • Anterior: Septal cartilage.

  • Posterior–superior: Perpendicular plate of ethmoid.

  • Posterior–inferior: Vomer.

  • All three articulate, forming midline partition.

• Lateral Wall major elements

  • Ethmoid bone contributes superior & middle nasal conchae.

  • Inferior nasal concha = independent bone.

  • Additional contributions: maxilla, palatine, lacrimal, sphenoid.

Lateral Wall Structures: Conchae (Turbinates) & Surface Area

• Three curved shelves project medially:

  • Superior concha (ethmoid).

  • Middle concha (ethmoid).

  • Inferior concha (separate bone).

• Covered by richly vascular nasal mucosa.

• Create turbulence → air swirls, maximizing contact with mucosa.

• High susceptibility to swelling during URIs & sinusitis, producing stuffiness.

Recesses & Meatuses (Drainage Corridors)

• Spheno-ethmoidal recess

  • Located above superior concha, between it & sphenoid body.

  • Drainage point of sphenoid sinus.

• Meatus = space beneath each concha:

  • Superior meatus (under superior concha)

  • Receives posterior ethmoidal air cells (2 openings typically).

  • Middle meatus (under middle concha) – most complex

  • Semilunar hiatus (curved groove on lateral wall).

    • Opening of maxillary sinus.

  • Ethmoidal infundibulum (superior extension of hiatus)

    • Continues as frontonasal duct → frontal sinus.

  • Ethmoidal bulla ("bubble")—prominence of middle ethmoidal cells.

    • Drains 2–3 middle ethmoidal air cells.

  • Inferior meatus (under inferior concha)

  • Contains opening of nasolacrimal duct → tears from orbit.

Vascular Supply

• Four main arterial sources create rich anastomotic network:

  • Anterior ethmoidal artery (ophthalmic) → anterior septum & lateral wall.

  • Posterior ethmoidal artery (ophthalmic) → superior septum & superior concha.

  • Sphenopalatine artery (terminal branch of maxillary) → posterior septum, middle & inferior conchae.

  • Facial artery (via superior labial branches) → anterior vestibule & external nose.

• Kiesselbach (Little’s) Area

  • Located on anterior inferior septum.

  • Convergence of all four arterial territories.

  • Most common site of epistaxis; chronic cases may be treated with cauterization.

Innervation

• Sensory (general):

Maxillary nerve (V2) – majority.

• Nasopalatine n. → septum.

• Posterior superior & posterior inferior lateral nasal branches → lateral wall.

• Ophthalmic nerve (V1)

• Anterior ethmoidal n. → anterior septum & lateral wall after passing through ethmoid.

• Special sensory (. ):

  • Olfactory nerve (CN I) fibers traverse cribriform plate to olfactory mucosa in roof.

• Autonomics (not detailed in transcript but implicit): carried via V2 branches from pterygopalatine ganglion.

Paranasal Sinuses (Contextual Review)

• Air-filled, mucosa-lined spaces continuous with nasal cavity; lighten skull, condition air, resonate voice.

• Sphenoidal sinus: drains into spheno-ethmoidal recess.

• Frontal sinus: drains via frontonasal duct → ethmoidal infundibulum → middle meatus.

• Ethmoidal cells

  • Posterior → superior meatus.

  • Middle → ethmoidal bulla (middle meatus).

  • Anterior → frontonasal duct path (middle meatus).

• Maxillary sinus: largest; opens high on medial wall into semilunar hiatus (middle meatus).

Clinical Correlations & Practical Points

• Swollen conchae = common cause of nasal obstruction during colds & sinusitis.

• High vascularity explains efficacy of topical meds (e.g., decongestants) & risk of epistaxis.

• Maxillary sinus drainage opening positioned superiorly → poor natural drainage when head upright → predisposition to infection.

• Deep sniff reflexively increases olfactory airflow, maximizing odorant exposure.